A head-mounted display (HMD) that the user puts on the head for, for example, viewing images is known. For example, as one of the HMDs, there is known an HMD including image display surfaces and display elements for right and left eyes (see, PTL 1). The HMD having such a configuration can display images having a parallax to the left and right eyes of the user through the left and right display surfaces, and hence can present three-dimensional (3D) images without crosstalk.
Meanwhile, also in an endoscope apparatus and the like used for medical purposes, a practical use of a 3D endoscope apparatus that can present 3D images is in consideration. An endoscopic surgery is less invasive for patients than a general surgical operation, and hence is popular in recent years. However, an affected part(s) is checked only by images during a surgery, and hence it is sometimes difficult to perceive a depth with traditional two-dimensional (2D) images. Therefore, it is expected that connecting and using the HMD capable of providing 3D images to a 3D endoscope apparatus can realize a more correct and rapid endoscopic surgery while viewing realistic images of the affected part.